The present invention relates to a starter for a Vee twin internal combustion engine including an electric starter motor and a gearing assembly coupled thereto as set forth in the preamble of claim 1.
The Vee twin internal combustion engine in the present context is a two-cylinder engine in a Vee arrangement intended for use in motorcycles. Saving weight in such an engine is of prime importance in the present context since a lightweight engine enhances handling the motorcycle powered thereby. When such a motorcycle is put to use, for instance, in cross-country sports events there is also the risk of damage when the engine is fitted with components exposed, for example, to impact by stones and grit thrown up by the front wheel of the motorcycle.
Hitherto, the motor of an electric starter on such a Vee twin engine was arranged either ahead of or behind the engine, as viewed in the forward direction, where it is exposed either to stone and grit impact or heat given off by the engine. Apart from this, this arrangement results in the design lacking compactness, since a starter motor arranged ahead of the engine increases the room needed in the frame of the motorcycle for locating the Vee twin engine and a starter motor arranged behind the rear cylinder, as viewed in the forward direction, requires a relatively long distance for communicating the torque from the starter motor to the crankshaft of the Vee twin engine.
Known from U.S. Pat. No. 2,335,186 A is an internal combustion engine in a Vee arrangement for an aircraft in which an electric starter motor is arranged in the Vee-shaped interspace between the cylinders and above the crankshaft. This starter motor is coupled via a gearing assembly to the crankshaft for communicating the drive torque.
The present invention is thus based on the objective of eliminating the aforementioned disadvantages by devising a starter for a Vee twin internal combustion engine wherein the starter motor is arranged outside of the region exposed to stone and grit impact and which enables a more compact arrangement of the Vee twin engine of the motorcycle frame.
The invention devised for achieving this objective comprises the features as set forth in claim 1. Advantageous aspects thereof read from the further claims.
In accordance with the invention a starter for a Vee twin internal combustion engine is now provided with an electric starter motor and a gearing assembly coupled thereto for communicating a torque output by the starter motor to a crankshaft of the engine and an overrunning clutch arranged between the gearing assembly and crankshaft, the starter motor and gearing assembly being arranged in the Vee-shaped interspace between the cylinders above the crankshaft. This arrangement results in the starter motor now being located outside of the region exposed to stone and grit impact whilst significantly reducing the room required for mounting the Vee twin engine in the frame of the motorcycle as compared to known arrangements.
According to the invention it is provided for that the gearing assembly has arranged above the crankshaft an intermediate shaft for communicating the torque output by the starter motor to the crankshaft and the intermediate shaft additionally being configured for balancing of masses and moments of first order. For this purpose a gearwheel may be rotatably mounted on the intermediate shaft, by which the torque output is communicated to the crankshaft.
This configuration of the intermediate shaft achieves a function concentration so that, as compared to known Vee twin engines, a reduction in weight is now achieved thanks to the starter in accordance with the invention for the Vee twin engine equipped therewith. This is due to the fact that the torque is now communicated from the starter motor to the crankshaft of the engine via a gearwheel mounted on the intermediate shaft and the intermediate shaft simultaneously serving as the balancer shaft of the engine which thus now requires no separate balancer shaft with the corresponding bearing locations as is the case with known Vee twin engines. Now, in accordance with the invention the function of balancing of masses and moments of first order is integrated in the intermediate shaft of the starter.
For this purpose it is provided for that on the intermediate shaft for balancing of masses and moments of first order a crank arm shaped or web-shaped balance mass is fixedly located both axially and rotatively at one axial end portion each of the intermediate shaft so that the web-shaped balance mass is located outside of or also between the webs of the crankshaft of the Vee twin engine.
A further means of saving space and thus enhancing the compactness of the Vee twin engine equipped with the starter in accordance with the invention is achievable by the intermediate shaft comprising at least one sprocket for driving a timing chain for actuating the valve gear of the internal combustion engine. This means in other words that the intermediate shaft may comprise two timing chain sprockets, each of which drives a timing chain for the camshaft drive of the front and rear cylinder head of the internal combustion engine equipped with the starter in accordance with the invention.
Equipping a liquid-cooled Vee twin engine with the starter in accordance with the invention now makes it possible to provide an impeller fixedly located axially and rotatively at one axial end of the intermediate shaft for pumping a coolant of the internal combustion engine. Integrating the coolant pumping function of such a liquid-cooled internal combustion engine in the intermediate shaft of the starter now makes it possible to eliminate two further bearing locations, namely the coolant pump shaft bearings, as compared to known engine concepts. This, together with the integration of the function for balancing free mass and moment forces in the intermediate shaft not only saves weight, it also reduces consumption, since as compared to known engine concepts several bearing locations as a source of friction can now be eliminated.
In another further embodiment of the starter in accordance with the invention it is provided for that for venting the crankcase of the internal combustion engine the intermediate shaft comprises a hole drilled substantially through the full axial length thereof, transversely to which at one axial end of the intermediate shaft a full-length hole is drilled crosswise for centrifugal engine oil scavenging.
Now, any overpressure building up in the crankcase due to blow-by in the combustion chambers of the Vee twin engine and due to the oscillating movement of the pistons in the cylinder liners in the crankcase can be relieved via the axial hole drilled lengthwise in the intermediate shaft, for example, into an air cleaner box communicating with a carburetion device of the Vee twin engine. Centrifugal engine oil scavenging through the intermediate shaft rotating, for example, at the speed of the crankshaft and the hole drilled crosswise thereto prevents the engine oil from gaining access to the air cleaner box.
It is also possible to implement engine oil scavenging by at least one drilled passage provided in a web-shaped balance mass on the intermediate shaft. This drilled passage thus runs from the longitudinal hole through the intermediate shaft and through the balance mass, resulting in a major length of the drilled passage developing a high speed at the end thereof due to rotation of the intermediate shaft for good engine oil scavenging and thus diminishing the load on the engine air cleaner with engine oil.
In this arrangement, the starter motor is now able to communicate its torque output directly to the gearwheel mounted on the intermediate shaft or indirectly via interposed gear shafts. By suitably selecting the transmission ratio between the starter motor and the crankshaft a comparatively low-power and thus small, compact electric starter motor is now sufficient for starting the Vee twin engine.
The overrunning clutch provided between the gearing assembly and crankshaft opens the non-positive connection between the starter motor and the crankshaft as soon as a predefined difference in speed is attained, i.e. once the Vee twin engine has been started, when its speed is higher than that of the crankshaft prompted by the starter motor before the engine is started.